American Society of Radiologic Technologist (ASRT) Practice Exam

How does an increase in kVp affect the keV of the characteristic interaction?

1. Increasing kVp slightly increases keV.

2. Increasing kVp decreases keV.

3. Doubling kVp doubles keV.

4. Increasing kVp does not affect the keV of the interaction.

The correct answer is: Increasing kVp does not affect the keV of the interaction.

The correct choice is that increasing kilovoltage peak (kVp) does not affect the keV of the characteristic interaction. Characteristic radiation is produced when an incident electron knocks out an inner-shell electron in a target atom, causing instability. The atom then shifts an outer-shell electron to fill the vacancy, releasing energy in the form of x-rays. The energy of these characteristic x-rays is determined by the difference between the binding energies of the electrons in the respective shells involved in the transition and is thus characteristic of the target material itself, regardless of the kVp applied. While increasing kVp increases the overall energy of the electrons in the beam, it does not change the energy of the characteristic x-rays produced because those energies remain fixed based on the atomic structure of the target material. Therefore, kVp influences the quantity and overall quality of the x-ray beam (including both characteristic and bremsstrahlung radiation), but the specific energy levels of characteristic x-rays do not change with kVp adjustments.